Rishi Sunak and Gillian Keegan are under growing pressure over the crumbling concrete closing schools, as the Education Secretary claimed others had failed to tackle the crisis in a sweary outburst.
In criticism caught on camera after an interview on Monday, a frustrated Ms Keegan hit out.
Ms Keegan went on to admit to being on holiday in Spain in the run up to ordering more than 100 schools and colleges in England to make complete or partial closures.
Earlier in the day, the Prime Minister admitted hundreds more schools could be affected by the reinforced autoclaved aerated concrete (Raac) issue.
He insisted that 95% of England’s schools were unaffected, leaving open the possibility that more than a thousand could still be impacted by the collapse-risk material.
Mr Sunak was also accused by a former top official at the Department for Education (DfE) of having declined a request for funding to rebuild more schools while he was chancellor.
Meanwhile, Ms Keegan promised MPs that a list of schools with confirmed Raac will be published “this week”.
The Prime Minister’s official spokesman rebuked the Education Secretary, saying the language she was caught on camera using “obviously is not acceptable”.
In a follow-up interview, Ms Keegan apologised for her “choice language” and said it was an “off-the-cuff remark”.
She blamed the interviewing journalist Daniel Hewitt for her frustration, saying he had been “pressing me quite hard” and claimed he was “making out it was all my fault”.
Ms Keegan insisted her criticism, which could have been interpreted as being targeted at Conservative colleagues, was about “nobody in particular”.
Mr Sunak was satisfied with her apology and continued to support her as Education Secretary, his spokesman said.
Aides later admitted that Ms Keegan was holidaying with family in Spain in the six days before announcing the closures to schools on Thursday.
She defended the trip, saying she continued to chair a response team while on the continent for her father’s birthday – and always planned to come back if investigations raised concerns.
“I came back straight away – well actually I had to wait a day because of the air traffic control issue,” she added to Sky’s Politics Hub.
Pupils face being taught in temporary classrooms, on different sites or even forced into pandemic-style remote lessons under the guidance issued as children prepared to return from the summer break.
Jonathan Slater, who was permanent secretary at the DfE between 2016 and 2020, said the Treasury knew there was a “critical risk to life” if the schools programme was not funded.
Mr Slater said up to 400 schools a year need to be replaced, but the DfE got funding for 100 while he was the senior official, which was “frustrating”.
He told BBC Radio 4’s Today programme: “The actual ask in the spending review of 2021 was to double the 100 to 200 – that’s what we thought was going to be practical at first instance.
“I thought we’d get it, but the actual decision that the chancellor took in 2021 was to halve the size of the programme.”
But Mr Sunak told reporters Mr Slater’s attack on his record was “completely and utterly wrong”.
The Prime Minister insisted that 50 schools a year was in line with what had taken place over the previous decade.
Mr Sunak acknowledged the timing of the announcement was “frustrating” and said that “95% of those schools won’t be impacted by this”.
If, as Mr Sunak said, 5% of schools are impacted, that would mean 1,100 are affected.
Downing Street said the total number was expected to be in the hundreds rather than the thousands.
Shadow education secretary Bridget Phillipson said: “The defining image of 13 years of the Conservative-run education system will be children sat under steel girders to stop the roof falling in.”
She said Mr Sunak “bears huge culpability for his role in this debacle”, adding: “Ministers need to come clean about the number of schools affected, what they knew, and when they knew, about the risks posed by Raac so that parents can be reassured their children are safe at school.”
Schools in Scotland, Wales and Northern Ireland are also being assessed for Raac.
The Scottish Government has said it is present in 35 schools, but that none poses an “immediate risk” to pupil safety.
The Welsh Government said two schools on Anglesey which had been due to open for the autumn term on Tuesday would be closed temporarily.